1. Technical Field
The present invention relates to a vibration damping device which suppresses vibration generated by a base material so that noise emitted from the base material is reduced, and a bucket for a construction machine.
2. Description of Related Art
In recent years, low noise levels have been required in construction machinery, especially in the case of nighttime work and in residential areas, and legal noise regulations which restrict noise to fixed levels or lower have also been enacted in various countries. For example, in the case of hydraulic excavators equipped with work equipment including buckets, it has been confirmed by experiment that such buckets are the main source of noise. It has been claimed that approximately 80% of the noise emitted from such work equipment is noise emitted from buckets.
Accordingly, attempts have been made to attach vibration damping materials to buckets in order to suppress the vibration that is generated in the buckets, especially the side plates of the buckets, and thus reduce the noise that is emitted from these side plates. Vibration damping materials used in such cases have generally been materials called viscoelastic materials, such as rubber, resins, asphalt or the like.
However, construction machinery is commonly used to perform work under harsh conditions, with the work equipment exposed to earth, sand and the like, and if vibration damping materials consisting of viscoelastic materials are attached to the work equipment, the problem of insufficient durability arises. Furthermore, such viscoelastic materials are generally constrained by metal plates, and in cases where these metal plates are repaired by welding, the problem of burning of the viscoelastic materials also arises. Since such viscoelastic materials are expensive, the problem of high cost of noise countermeasures also arises.
Accordingly, in response to the demand for the development of a low-cost vibration damping device which has a high durability and involves no burning during repair, the assignee of the present application has already developed a laminated plate and filed a patent application for this plate, which has been disclosed in Japanese Patent Application Laid-Open No. 2000-219168 (or U.S. Pat. No. 6,332,509), Japanese Patent Application Laid-Open No. 2002-48188 and the like. With respect to the abovementioned publications, an explanation will be made with reference to FIG. 2. A plurality of thin steel plates 21 (hereafter referred to as “thin plates 21”) are laminated on the side plate 11 of the bucket, thus forming laminated plate 20. It is indicated that relatively thick steel plate 30 (hereafter referred to as “protective plate 30”) that protect the thin plates 21 is further superimposed on top of the laminated plate 20, and that the periphery 20a (see FIG. 1) is fastened by performing all round fillet welding or intermittent fillet welding, or by performing intermittent plug welding, bolt fastening or the like. Since the laminated plate 20 is constructed from an inexpensive material that has a high durability and is resistant to burning, i.e., steel, the problem points encountered in conventional viscoelastic materials can be solved.
The mechanism whereby the laminated plate 20 suppresses the vibration generated in the side plate 11 and thus reduces the noise emitted from the side plate 11 is described in the abovementioned publications; this mechanism will be described with reference to FIGS. 4A and 4B. Specifically, when the side plate 11 vibrates, this vibration is transmitted to the laminated plate 20, so that the thin plates 21, 21′ constituting the laminated plate 20 undergo deformation. In the laminated plate 20 in which numerous thin plates 21, 21′ are superimposed, the amount of deformation differs in each layer. Specifically, the respective curvature radii r1 and r2 differ in adjacent thin plates 21, 21′. Accordingly, in the thin plates 21, 21′ in which the original displacement was X (see FIG. 4A), the displacement respectively varies to X+ΔX2 and X+ΔX1 as a result of the microscopic displacement caused by the vibration, so that a relative displacement of ΔX2−ΔX1 is generated between the two thin plates 21 and 21′. This relative displacement of ΔX2−ΔX1 causes the generation of a frictional force (hereafter referred to as an “inter-layer frictional force”) between the thin plates 21 and 21′. The vibration energy generated in the side plate 11 is converted into thermal energy by this inter-layer frictional force. As a result, the vibration generated in the side plate 11 is suppressed so that the noise emitted from the side plate 11 is reduced.
Accordingly, as is shown in FIG. 4B, the independent deformation of the thin plates 21 and 21′ so that a relative displacement of ΔX2−ΔX1 is generated is a condition for performing vibration damping. Conversely, therefore, if the two thin plates 21 and 21′ are fastened in place so that these plates function as an integral unit, the independent deformation is hindered, so that there is absolutely no generation of a relative displacement or very little generation of a relative displacement; as a result, no vibration damping effect is obtained, or an extremely small vibration damping effect is obtained.
This will be explained with reference to FIG. 1. In a conventional device, the peripheries 20a of the laminated plate 20 are fastened to the side plate 11 by welding or the like. However, in a common conventional structure, the interior parts (used in the sense of the portions other than the peripheries 20a) of the laminated plate 20 are not fastened to the side plate 11, so that the independent deformation of the respective layers is not impeded, thus producing a high vibration damping effect. However, it has become clear that the following problems arise if the interior parts of the laminated plate 20 are not fastened.
First of all, gaps are generated between the thin plates 21 and 21′ that constitute the laminated plate 20, and gaps are generated between the side plate 11 and the laminated plate 20, by the thermal strain that is generated in the welding process during manufacture. As a result, the frictional force that should inherently occur between the thin plates 21 and 21′ during the vibration of the side plate 11 either does not occur or occurs to only a very slight extent, so that a vibration damping effect is either completely absent or present to a very slight extent.
Secondly, during actual work performed by construction machinery, excessively large external forces are commonly applied to the side plate 11 as a result of the bucket striking rocks and the like. Consequently, the laminated plate 20 in which the internal portions are not fastened and only the peripheries 20a are fastened is easily caused to “float upward” by these excessive external forces. In other words, the laminated plate 20 separates from the side plate 11, and the thin plates 21 and 21′ separate from each other. As a result, the inter-layer frictional force that should be generated between the thin plates 21 and 21′ during the vibration of the side plate 11 is either not generated at all or generated only to a very slight extent, so that a vibration damping effect is either not obtained at all or obtained only to a very slight extent.
Thus, in order to obtain a high vibration damping effect, it is desirable that the internal portions of the laminated plate 20 not be fastened, so that the deformation of the thin plates 21 is not impeded. However, if the internal portions of the laminated plate 20 are not fastened, “floating” occurs as a result of thermal strain during the manufacture of the bucket and external forces during the use of the bucket, so that the problem of a loss of the vibration damping effect arises.
Furthermore, the types of buckets used in construction machinery vary widely according to the size, specifications and working applications of the construction machinery. When the present inventors performed experiments on various types of buckets with different sizes, shapes, dimensions and the like, and confirmed the effect obtained by attaching laminated plate to the side plate, the inventors discovered that the effect varies according to the type of bucket involved. Specifically, depending on the type of bucket involved, there are cases in which the contribution of the side plate to noise is large, and cases in which the contribution of the side plate to noise is small and the contribution of the bottom plate to noise is large. The following countermeasures are conceivable in such cases.
(1) The contribution to noise is measured for various types of buckets, and in the case of buckets in which the contribution of the bottom plate to noise is large, noise countermeasures are taken with respect to the bottom plate as well.
(2) Noise countermeasures are uniformly taken in the bottom plate for all types of buckets.
However, in cases where the method of the abovementioned (1) is adopted, noise experiments and the like must be performed each time that a bucket is newly designed, which involves considerable trouble. Furthermore, in cases where the method of the abovementioned (2) is adopted, it is necessary to add parts used for noise countermeasures even in the case of buckets that do not require noise countermeasures, so that the cost is increased.
Accordingly, it is desirable to set clear standards for the requirement of noise countermeasures with respect to the bottom plate, and to perform noise countermeasures using the minimum required effort for the minimum required buckets among the various types of buckets, without performing noise experiments or the like. On the other hand, in cases where noise counter measures are performed on the bottom plates of buckets, there are instances in which laminated plate cannot be attached (unlike the case of the side plate). Specifically, during the work performed by construction machinery, the bottom plate of the bucket often has occasion to strike rocks or the like; accordingly, compared to the side plate, the bottom plate is more frequently subjected to excessive external forces, so that the bottom plate is subjected to severe wear. Accordingly, there is a danger that the laminated plate attached to the bottom plate will be destroyed or separated, and is therefore deficient in durability. Furthermore, in cases where laminated plate is attached to the bottom plate, the problem of increased cost also arises.
Therefore, in order to avoid such problems, it is conceivable that vibration damping might be performed while increasing the rigidity of the bottom plate by reinforcing the bottom plate with a reinforcing material. Depending on the type of bucket involved, there may be buckets in which reinforcing members with a large thickness (called wear plates) are attached to the portions of the side plate of the bucket that are close to the bottom plate, and it is conceivable that vibration damping of the bottom plate might be performed by increasing the thickness of such wear plate. However, increasing the thickness of the wear plate leads to an increase in the weight of the bucket, and thus has a deleterious effect on the performance of the construction machinery. Specifically, when the weight of the bucket is increased, the inertial moment of the work equipment increases, so that it is necessary to increase the counter-weight by a corresponding amount. When the counter-weight is increased, the problem of an increase in the turning radius of the construction machinery arises. Accordingly, it is desirable that reinforcement of the bottom plate of the bucket be performed with the minimum necessary increase in weight.
Furthermore, a vibration damping device using a laminated plate in which a plurality of plates are partially coupled is known as a vibration damping device which has an effect on noise reduction in the machinery, and which is compact and superior in terms of durability. Furthermore, bolt fastening, plug welding or complete-periphery welding is used as such partial coupling (for example, see the abovementioned Japanese Patent Application Laid-Open No. 2002-48188, pages 3 through 5, and FIGS. 1 through 8). In vibration damping devices using the laminated plate since the laminated plate is partially coupled to the noise generating parts (vibrating parts), very small positional deviations or gaps are generated between the vibrating parts and laminated plate and between the plates that make up the laminated plate when the noise generating parts vibrate. Since these very small positional deviations and gaps successively arise while constantly varying, friction and impacts between the plates are repeated. Accordingly, the vibrational energy of the noise generating parts is converted into thermal energy by the friction and impacts, and is diffused, so that the vibration can be reduced, thus reducing the noise.
However, in the case of such conventional techniques, problems such as those described below arise. Specifically, in cases where such techniques are applied to the side plate of the bucket in a hydraulic excavator, if bolt fastening or plug welding is used for the partial coupling of the side plate and laminated plate, rain water enters via the end surfaces of the laminated plate so that rusting occurs between the plates, thus causing a drop in the vibration damping performance. If all round welding of the end surfaces of the laminated plate is used for the partial coupling of the side plate and laminated plate in order to prevent rusting, the plates forming the laminated plate are mutually constrained, so that the generation of very small positional deviations and the like is impeded, thus causing a drop in the vibration damping performance.
The application of laminated plate such as shown in FIG. 29 to the side plates of the bucket is conceivable as one example of a technique that can protect the welded parts of the laminated plate. In the bucket 101, side plates 103, 103 are respectively welded to both sides of a bottom plate 102 which is bent into substantially a C shape. Furthermore, edge plates 104, 104 and 105 are respectively welded to the side plates 103, 103 and bottom plate 102 to form the opening part of the bucket 101. A plurality of teeth 106 are mounted on the edge plate 105. Pin bosses 107 which are connected to the work equipment of the hydraulic excavator are disposed on the end part located on the opposite side from the tooth attachment part of the bottom plate 102. Wear plate 108 is disposed on the peripheral parts of the outside surfaces of the side plate 103 so that the wear plate 108 runs along the bottom plate 102. Laminated plate 150 is bonded to the outside surfaces of the side plate 103 so that the laminated plate 150 is surrounded by the edge plate 104 and wear plate 108. As is shown in FIG. 30, the laminated plate 150 comprises an inner plate 151 consisting of a specified number of laminated thin steel plates, and an outer plate 152 with a specified thickness which is laminated on the outside of the inner plate 151, and which retains and protects the inner plate 151. These plates are bonded to the side plate 103 so that the side plate 103, inner plate 151 and outer plate 152 show substantially tight adhesion to each other. A gap d1 is formed between the laminated plate 150 and the wear plate 108 as welding margins for the welding of the laminated plate 150 and wear plate 108 to the side plate 103. Furthermore, as is shown in FIG. 31, a gap d2 is formed between the laminated plate 150 and the edge plate 104 as welding margins for the welding of the laminated plate 150 and edge plate 104 to the side plate 103. For example, as is shown in FIGS. 32A and 32B, both gaps d1 and d2 are embedded by repeating fillet welds twice. Specifically, laminated plate 150 is bonded to the side surface of the bucket 101 by all round welding.
As a result of the abovementioned construction, noise during excavation work can be reduced by the dissipation of vibrational energy by the inner plate 151 of the laminated plate 150 as thermal energy. Furthermore, the laminated plate 150 disposed on the side surfaces of the bucket 101 prevents the entry of rain water into the interior parts of the laminated plate as a result of the all round welding, and thus prevents the occurrence of rusting between the plates, so that the vibration damping performance can be maintained. Moreover, the edge plate 104 and wear plate 108 protect these welded parts from friction or impact with rocks and the like during excavation work; accordingly, wear and damage of the welded parts of the laminated plate 150 can be prevented, so that the durability of the laminated plate 150 can be improved.
However, the following problems are encountered even in cases where the abovementioned wear plate 108 is used.
(1) The laminated plate that converts the vibrational energy into thermal energy arising from friction between the plates, and thus dissipates this energy, shows an improved vibration damping performance as the number of points of constraint is reduced. However, the inner plate 151 of the laminated plate 150 is constrained around the entire periphery by all round welding of the periphery, so that the vibration damping performance drops. Conversely, in cases where the peripheries of the laminated plate 150 are intermittently welded in order to reduce the number of points of constraint and improve the vibration damping performance, rusting occurs as a result of the invasion of the interior parts by rain water.
(2) If specified gap d1 is not ensured between the laminated plate 150 and the wear plate 108 during manufacture, a sufficient welding quality cannot be obtained. Considerable work is required in order to position the inner plate 151 and outer plate 152 so that the gap d1 is ensured; as a result, the cost is increased.
(3) Since the volume of the welded parts is large, the cost increases with the amount of work that is required. Conversely, if the peripheries of the laminated plate 150 are intermittently welded in order to reduce the amount of welding, rusting occurs as a result of the invasion of the interior parts by rain water as in the case of the abovementioned (1).
(4) In order to prevent floating and deformation caused by thermal strain during continuous welding, it is necessary to effect a temporary attachment of the laminated plate 150 and side plate 103 at an extremely large number of points, so that considerable work is required, and the cost is increased.
Furthermore, as an example of another application in which laminated plate is bonded, there is an application in which laminated plate 160 (comprising a specified number of inner plates 161 and an outer plate 162) is bonded to the inclined plate 172 of the hopper 171 of a crusher 170 as shown (for example) in FIG. 33. In this case, it is conceivable that all round welding might be used in order to prevent foreign matter such as water or the like from invading the interior parts of the laminated plate. In this case as well, since the entire periphery of each of the inner plates 161 of the laminated plate 160 is constrained by all round welding as in the abovementioned (1), the vibration damping performance drops. Conversely, if the peripheries of the laminated plate 160 are intermittently welded in order to improve the vibration damping performance, rusting occurs as a result of the invasion of the interior parts by water and the like.